1. Technical Field
The present disclosure relates to electrosurgical devices suitable for use in tissue ablation applications and, more particularly, to electrosurgical devices with directional radiation patterns.
2. Discussion of Related Art
Treatment of certain diseases requires the destruction of malignant tissue growths, e.g., tumors. Electromagnetic radiation can be used to heat and destroy tumor cells. Treatment may involve inserting ablation probes into tissues where cancerous tumors have been identified. Once the probes are positioned, electromagnetic energy is passed through the probes into surrounding tissue.
In the treatment of diseases such as cancer, certain types of tumor cells have been found to denature at elevated temperatures that are slightly lower than temperatures normally injurious to healthy cells. Known treatment methods, such as hyperthermia therapy, heat diseased cells to temperatures above 41° C. while maintaining adjacent healthy cells below the temperature at which irreversible cell destruction may occur. These methods involve applying electromagnetic radiation to heat, ablate and/or coagulate tissue. Microwave energy is sometimes utilized to perform these methods. Other procedures utilizing electromagnetic radiation to heat tissue also include coagulation, cutting and/or ablation of tissue.
Electrosurgical devices utilizing electromagnetic radiation have been developed for a variety of uses and applications. A number of devices are available that can be used to provide high bursts of energy for short periods of time to achieve cutting and coagulative effects on various tissues. There are a number of different types of apparatus that can be used to perform ablation procedures. Typically, microwave apparatus for use in ablation procedures include a microwave generator, which functions as an energy source, and a microwave surgical instrument (e.g., microwave ablation probe) having an antenna assembly for directing the energy to the target tissue. The microwave generator and surgical instrument are typically operatively coupled by a cable assembly having a plurality of conductors for transmitting microwave energy from the generator to the instrument, and for communicating control, feedback and identification signals between the instrument and the generator.
There are several types of microwave antenna assemblies for the ablation of tissue, such as monopole, dipole and helical. In monopole and dipole antenna assemblies, microwave energy radiates perpendicularly away from the axis of the conductor. Monopole antenna assemblies include a single elongated conductor whereas a typical dipole antenna assembly includes two elongated conductors, which are linearly aligned and positioned end-to-end relative to one another with an electrical insulator placed therebetween. Helical antenna assemblies include a helically-shaped conductor connected to a ground plane. Helical antenna assemblies can operate in a number of modes, such as normal mode (broadside), in which the field radiated by the helix is maximum in a perpendicular plane to the helix axis, and axial mode (end fire), in which maximum radiation is along the helix axis.
A microwave transmission line typically includes a long, thin inner conductor that extends along a longitudinal transmission line axis and surrounded by a dielectric material and is further surrounded by an outer conductor around the dielectric material such that the outer conductor also extends along the transmission line axis. In one variation of an antenna, a length of transmission line is provided with a plurality of openings through which energy “leaks” or radiates away from the transmission line or coaxial cable. This type of construction is typically referred to as a “leaky coaxial” or “leaky wave” antenna. A leaky wave antenna is basically a waveguiding structure constructed so as to “leak” power along the length of the guiding structure.
During certain procedures, it can be difficult to assess the extent to which the microwave energy will radiate into the surrounding tissue, making it difficult to determine the area or volume of surrounding tissue that will be ablated.